Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.98   4.111%   $245.6811   $245.68   $245.70   $245.70  
  Purchase #2 $183.73   11.541%   $204.9343   $204.93   $204.95   $204.90  
  Purchase #3 $153.40   3.606%   $158.9316   $158.93   $158.95   $158.90  
  Purchase #4 $242.25   13.404%   $274.7212   $274.72   $274.70   $274.70  
  Purchase #5 $119.99   6.143%   $127.361   $127.36   $127.35   $127.40  
  Purchase #6 $156.70   11.542%   $174.7863   $174.79   $174.80   $174.80  
  Purchase #7 $36.93   5.177%   $38.8419   $38.84   $38.85   $38.80  
  7 purchase totals = $1,128.98       $1,225.2574   $1,225.25   $1,225.30   $1,225.20